For producing building-material coatings, frequently building-material coating agents are used which contain mineral binders such as cement or hydrated lime, fillers, such as sand or gravel, and optionally other additives. In order to improve the mechanical properties of the building-material coatings, fibers can be introduced, for example in the form of woven fabrics. For instance, in DE-A 2516916 or in DE-A 4216204, the production of building-material coatings is described in which, first, cement-based mortar mixtures are applied to a substrate and, in a separate step, woven fiber fabrics or nonwoven fiber fabrics, such as, for example, glass fiber fabrics or fiberglass gratings, are embedded in the mortar layer. This procedure requires, however, conceptually many working steps for applying the mortar layer and the fibers and is therefore complex.
In contrast, it is less complex to use fibers as a component of the building-material coating agent for producing fiber-reinforced building-material coatings. However, this procedure is limited, since building-material coating agents having relatively high contents of fibers or having relatively long fibers, for example longer than 10 mm, are not processable by the previously known methods, i.e. are not transportable, for example are not pumpable, or have an inhomogeneous distribution of the fibers in the building-material coating agents (what is termed “formation pockets”), which has disadvantageous effects on the properties of the building-material coatings. In order to be able to process building-material coating agents having a content of fibers of greater than five percent, according to Thomas Friedrich, BetonWerk International, No. 1, 2001, pages 126 to 134, it is necessary to use a spraying technique in which the building-material coating agent and fibers are conducted separately to a spray head in order to be applied into a formwork under pressure within a shared jet. However, even when this method is used, the processable amount of fibers in coating agents is still limited. Even in the case of this method, on application of building-material coating agents having relatively high fiber contents, pocket formation of occurs and, in association therewith, an impairment of the mechanical properties corresponding to obtainable building-material coatings. The abovementioned spray technique is also known, for example, from DE-A 5190217 for the application of asphalt, or from GB 1493547 or GB 910674 for producing glass fiber mats for composite components made of plastics material. A technical embodiment of the spray technique and a corresponding spray nozzle are described in DE-A 3336053.
A further problem in carrying out spray methods is the rebound occurring therein. Rebound designates the amount of building-material coating agent which, on application to a substrate, does not remain adhering to the substrate, but falls off and therefore must be disposed of as waste. The rebound in conventional methods is usually greater than 30% of the application. This is in particular a considerable economic disadvantage therefore for the use of fiber-modified building-material coating agents, since fibers such as, for example glass fibers, compared to the other components of the coating agents, are relatively expensive. In DE-A 2751661, a mechanical spray technique method is described in which chopped fiberglass is sprayed into a building-material coating agent stream and is then applied to a substrate. DE-A 2751661 does not contain any statements either, as to how the rebound could be reduced, or how fiber-reinforced building-material coatings with relatively high fiber contents could be processed. A further problem is that, in this manner, usually many fibers project out of the surface of the building-material coatings. The building-material coatings therefore do not have a uniform surface.